Method of forming coatings of metal and product thereof



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This invention relates to a method of coating articles with metal by cathode sputterin and the coated articles so produced.

he object of my invention is'to rovide 5 on various articles of manufacture a urable, non-corrosive, firmly adherent protective sure articularl in those cases in which electroplating in a uid electrolyte or the various methods of c emical plating have proved to be unsatisfactory. or example, metal coatings may be formed on glass by this method. Y Y With the above and other objects in v ew, the invention consists in the construction, combination and arrangement of' parts as, will be hereinafter more fully described.

It is known that when an electric discharge takesplace from a metal cathode in a sum ably evacuated space that portions of the cathode are torn off and carried away therefrom. This takes/ place at a'rate that is proportional to the square of the current as contrasted with electrolysis in aliquid e cotrolyte wherethe removal of metal is proportional to the first power of the current. As the metal so removed is in atomic form it is in such a physical condition that permits the particles to'approach a surface sufficientl close to come within the range ofso molecu r attraction, and hence'a tight,v alhe. as:

Thecathodic deposits of most substances are soft, but those formed by discharges most integral bond formed with face. 4

a from silicon or chromium cathodes are hard and dense. It is for this reason that I prefer 1 It is further known that the rate of deposition is much greater. in a space that contains an inert or a monatomic gas, such as mercury vapor, ar on or helium, and it is therefore desirable t at' one or more of these gases be present in the tube in which the coatings are formed.

A method of racticing my invention that f. has proved satlsfactory is to place the article to be coated in an air tight tube or chamber; having suitable electrodes therein one at least of which is made of the metal it is desired to deposit asa coating. The surface to be coveredis placed about two r temating current. .In this f is placed in the chamber, and the air is pum out until the chamber is practically devoid of any gas except the mercury vapor. Enough helium is then admitted to the cham-v ber to raise the pressure to a value at which a good electrical discharge occurs I when a potential of about five thousand volts is applied across the electrodes. 'Maintenance of this discharge for ap roximately eight hours, with the electrode that is made of the metal it is desired to deposit functioning as electrode for about one-half of that-time, results in a smooth, fine grained, dense de: posit on the surface of the article. If alternating current is used each electrode 1s the cathode for one-half the time, as mentioned above, and it is then conven-- lent to make both electrodes of material to be sputtered and place .two plates back to back, whereby that side of each plate that faces an electrode is covered with the metal. The electrodes need not be of the same metal, as the character and purity of the deposit 9 on a surfa'ce'facing one electrode is negligibly affected by the material of the opposite electrode. 1 Direct current can be used for the sputterg and the coatings are produced just as suc cessfully as, and more ra idly than, with alcase the material of the anode is unimportant.

It was found that coatings of silicon and chromium so formed were entirely unafiec'ted' by the application of any common acids or 5 lations of weght to size and freedom from.

warping, but ordinary brass plates tit from tarnishing under ordinary operatin conditions whi e aluminum plates rub 0 onto the crystals and. change their frequencies. Top plates made of either of the mentioned materials are very satisfactory when provided with a coating of silicon or chromium by the method herein disclosed.

While the application of my invention to a specific use has been set forth for purposes of illustration, it is to be understood that this is not to be interpreted as e limitation of the invention, as it finds many uses other than thet mentioned i It will be understood'thnt the above descri tion comprehends only the general and pre erred embodiment of my invention and that various changes in construction, proportion and errengement of parts mey be made within the scope of the appended claims without sscriiicmg any of the advantages of my invention.

lhe invention described herein may be menufectured end used by or for the Gov ernment of the United Stetes of America -tor governmentel purposes without the payment vapor, releasing one or more monatomic gases in said chamber to raise the pressure in said chamber to a magnitude at which the de-= sired discharge will pass, and passing a discharge between said electrodes until the requisite thickness of metal has been deposited on said object.

2. A method of electrodepositing metal, comprising the steps of disposing an ob'ect between electrodes in an air-tight chamber, one of which electrodes is made of the metal tobe deposited, exposing in said chamber a body of mercury having a free surface, evacuating said chamber until there is substantiuly no gas therein except mercury vapor, releasing helium gas in said chamber to raise the pressure in said chamber to a magnitude at which the desired discharge will pass and pessin e discharge between said electrodes until t e requisite thickness of metal has been deposited on seid object.

3. A method of electrodepositing metal, comprising the steps of disposing an object between electrodes in'an air-tight chamber, one of which electrodes is mode of the metnl to be deposited, exposing in said chamber body of mercury having n free surface, evec uating said chamber until there is substantially no gas therein except mercury vapor,

releesing helium gas in said chamber to raise the pressure in seid chamber to a magnitude at which the desired discharge will pass and passing a, discharge at e potential of substantially 5,000 volts for 21 period of about eight hours. i 

